• Choose a category
• All
• Classic-Fiction

}

}

return 0;

}

Programmers do this so often that they made a special addition to the for-loop for iterating over arrays. Edit the code to use this mechanism:

#import

int main(int argc, const char * argv[])

{

@autoreleasepool {

// Create three NSDate objects

NSDate *now = [NSDate date];

NSDate *tomorrow = [now dateByAddingTimeInterval:24.0 * 60.0 * 60.0];

NSDate *yesterday = [now dateByAddingTimeInterval:-24.0 * 60.0 * 60.0];

// Create an array containing all three (nil terminates the list)

NSArray *dateList = [NSArray arrayWithObjects:now, tomorrow, yesterday, nil];

for (NSDate *d in dateList) {

NSLog(@"Here is a date: %@", d);

}

}

return 0;

}

This type of loop is known as fast enumeration, and it is an extremely efficient way to walk through the items in an array. There is one restriction: you may not add to or remove from the array while enumerating over it.

NSMutableArray

Arrays come in two flavors:

An instance of NSArray is created with a list of pointers. You can never add or remove a pointer from that array.

An instance of NSMutableArray is similar to an instance of NSArray, but you can add and remove pointers. (NSMutableArray is a subclass of NSArray. More about subclasses in Chapter 18.)

Change your example to use an NSMutableArray instance and methods from the NSMutableArray class:

#import

int main(int argc, const char * argv[])

{

@autoreleasepool {

// Create three NSDate objects

NSDate *now = [NSDate date];

NSDate *tomorrow = [now dateByAddingTimeInterval:24.0 * 60.0 * 60.0];

NSDate *yesterday = [now dateByAddingTimeInterval:-24.0 * 60.0 * 60.0];

// Create an empty array

NSMutableArray *dateList = [NSMutableArray array];

// Add the dates to the array

[dateList addObject:now];

[dateList addObject:tomorrow];

// Put yesterday at the beginning of the list

[dateList insertObject:yesterday atIndex:0];

for (NSDate *d in dateList) {

NSLog(@"Here is a date: %@", d);

}

// Remove yesterday

[dateList removeObjectAtIndex:0];

NSLog(@"Now the first date is %@", [dateList objectAtIndex:0]);

}

return 0;

}

Challenges

Create a new Foundation Command Line Tool named Groceries. Start by creating an empty NSMutableArray object. Then add several grocery-like items to the array. (You’ll have to create those, too.) Finally, use fast enumeration to print out your grocery list.

This next challenge is, well, more challenging. Read through the following program, which finds common proper names that contain two adjacent A’s.

#import

int main (int argc, const char * argv[])

{

@autoreleasepool {

// Read in a file as a huge string (ignoring the possibility of an error)

NSString *nameString

= [NSString stringWithContentsOfFile:@"/usr/share/dict/propernames"

encoding:NSUTF8StringEncoding

error:NULL];

// Break it into an array of strings

NSArray *names = [nameString componentsSeparatedByString:@"\n"];

// Go through the array one string at a time

for (NSString *n in names) {

// Look for the string "aa" in a case-insensitive manner

NSRange r = [n rangeOfString:@"AA" options:NSCaseInsensitiveSearch];

// Was it found?

if (r.location != NSNotFound) {

NSLog(@"%@", n);

}

}

}

return 0;

}

The file /usr/share/dict/propernames contains common proper names. The file/usr/share/dict/words contains regular words (not proper names). Now write a program based on the one above that finds common proper names that are also regular words. For example, “Glen” is a guy’s name, and “glen” is a narrow valley.

When a computer orders strings, it typically considers uppercase letters as coming before lowercase letters. To do a comparison that ignores the case, use the method caseInsensitiveCompare:.

NSString *a = @"ABC";

NSString *b = @"abc";

if ([a caseInsensitiveCompare:b] == NSOrderedSame) {

NSLog(@"a and b are equal");

}

if ([a caseInsensitiveCompare:b] == NSOrderedAscending) {

NSLog(@"a comes before b");

}

if ([a caseInsensitiveCompare:b]